1. Field of the Invention
The present invention relates to a facsimile adapter, and specifically to a facsimile adapter for adding Group 4 ("G4": International Telecommunications Union (ITU-)-T recommendation T.6) capability to an existing facsimile machine provided with Group 3 ("G3": ITU-T recommendation T.4) capability.
2. Description of the Related Art
Currently, common facsimile communication is G3 communication whereby digital facsimile data is converted to analog audio signals by a modem, and transmitted over a common public telephone line. G4 facsimile communication whereby a digital data line, or more specifically an ISDN (Integrated Services Digital Network), is used to transmit digital data in digital form is growing. In order to perform G4 facsimile communication, a dedicated facsimile machine (typically, such a machine is also capable of performing G3 facsimile communication, as well) is generally purchased, but an adapter (a G4 facsimile adapter) is also available to add G4 communication capability to a conventional G3 facsimile machine.
An example of the essential structure of a conventional G4 facsimile adapter which is attached to an existing facsimile machine with G3 capability will be described below in reference to FIG. 7 of the accompanying drawings.
In FIG. 7, a reference numeral 100 designates a facsimile machine with G3 capability to which a G4 facsimile adapter 110 is connected by buses. In other words, the data bus 103 of the existing G3 facsimile machine 100 and the data bus 25 of the G4 facsimile adapter 110 are connected. A reference numeral 2 denotes an ISDN (digital data line), and 3 denotes a public switched telephone network (a normal analog audio line or network).
Since the structure of the G3 facsimile machine 100 is known, only G3 modem 101 and NCU (Network Control Unit) 102 are shown in FIG. 7. When the facsimile machine 100 transmits data to a remote device (not shown), digital facsimile data generated from an element (not shown) is converted into analog audio signals by G3 modem 101. These audio signals are transmitted to the public switched telephone network 3 by NCU 102. Further, when the facsimile machine 100 receives data, NCU 102 receives analog audio signals from the public switched telephone network 3, and these signals are converted to digital facsimile data by G3 modem 101.
The G4 facsimile adapter 110 is comprised of an ISDN interface unit 11 which provides interface capability with the ISDN 2, an audio signal CODEC unit 12 which converts between analog signals and digital data, a G3 modem 16 which converts between facsimile data and audio signals, a G4 facsimile unit 20, and CPU 13 which controls the entire structure.
The ISDN interface unit 11 includes an S-interface function and an LAP-D (Link Access Procedure on D-Channel) function. S-interface means S-point interface, and includes protocol processing capability, maintenance capability, and interface capability. LAP-D function controls the protocol for ISDN channel D.
The G4 facsimile unit 20 is comprised of LAP-B (Link Access Procedure Balanced mode) unit 21, EP-ROM 22 and S-RAM 23, all of which are attached to the data bus 25 connecting the ISDN interface unit 11 and the G3 facsimile machine 100.
The LAP-B unit 21 controls the protocol for ISDN channel B, and actually transmits the data. EP-ROM 22 and S-RAM 23 are used for storage of programs used by the CPU 13, control data, intermediary data, and the like.
The conventional G4 facsimile adapter 110 is designed to be connected to the data bus 103 of the existing G3 facsimile machine 100. Even when G3 facsimile communication utilizes ISDN, the G4 adapter's G3 modem 16 is used instead of the G3 modem 101 of the existing G3 facsimile machine 100. Since this creates the obvious necessity of changing the G3 communication originally adapted to the existing G3 facsimile machine 100, the associated software must be changed.
Furthermore, the operation performed by the user also must change in order to use the G3 modem 16 of the G4 facsimile adapter 110 even when the user utilizes the existing G3 facsimile machine 100 to perform G3 facsimile communication. This can cause difficulties for the user. Further still, since the G3 modem 16 of the G4 adapter 110 must be used instead of the G3 modem 101 already provided on the existing G3 facsimile machine 100, the G3 modem 101 provided on the existing G3 facsimile machine 100 becomes useless. Put in another way, if the G3 modem 101 already provided in the existing G3 facsimile machine 100 could be used instead of providing a G3 modem 16 in the G4 adapter 110, it would be possibly to reduce the manufacturing costs of the G4 adapter 110.
Japanese Patent Application, Laid-Open Publication No. 8-331296 discloses a system which simply combines a G3 facsimile machine with a G4 facsimile machine.